The present invention relates to a vibratory actuator having a piezoelectric element.
Vibratory actuators having piezoelectric elements (electromechanical transducer elements) used for various electric devices have been known. This type of a vibratory actuator includes a piezoelectric element having piezoelectric layers and electrode layers provided so as to interpose the respective piezoelectric layers therebetween. In the vibratory actuator, an electric field is applied to the piezoelectric layers to induce desired vibration in the piezoelectric layers, and thus driving force is output.
Examples of such vibratory actuators includes a vibratory actuator in which an electrode layer provided on one of the principal surfaces of a piezoelectric layer is configured by four split electrodes disposed in four regions which are obtained by halving the principal surface respectively in the longitudinal and the lateral directions, and an electrode layer provided on the other principal surface of the piezoelectric layer is also configured by four split electrodes in a similar way.
For example, a vibratory actuator according to Japanese Patent Publication No. 2008-278710 (referred to hereinafter as Patent Document 1) includes four split electrodes, such as one described above, on one and the other principal surfaces of a piezoelectric layer in order to induce a first-order mode of expanding/contracting vibration (stretching vibration, or longitudinal vibration) and a second-order mode of bending vibration (lateral vibration) in the piezoelectric layer by full-bridge driving or push-pull driving.
In the piezoelectric element having such split electrodes, in order to supply power to eight split electrodes in total on the both principal surfaces of a piezoelectric layer, each of these eight split electrodes needs to be connected to a connection line such as a wire or a flexible cable. In this case, each connection line acts as a load and thus disturbs vibration of the piezoelectric element, which may reduce the efficiency of vibratory actuator.
Therefore, a vibratory actuator described in Patent Document 1 has a configuration in which two split electrodes disposed along a diagonal direction, among the split electrodes in a same electrode layer, are connected together approximately at the center of the electrode layer using a connection electrode expanding in the diagonal direction. Since a same drive voltage is applied to the two split electrodes disposed along a diagonal direction in a same electrode layer, such connection in the same electrode layer allows the connection lines for one split electrode to be eliminated.
However, if the two split electrodes disposed along a diagonal direction in each electrode layer are connected together using a connection electrode expanding in the diagonal direction, only the two split electrodes disposed along one diagonal direction can be connected together in one electrode layer. Each electrode layer includes two pairs of split electrodes disposed along diagonal directions, and in addition, there are two types of electrode layers: one is a positive type of electrode layer provided on one principal surface of a piezoelectric layer, and the other is a negative type of electrode layer provided on the other principal surface of the piezoelectric layer. Thus, a piezoelectric element included in a vibratory actuator described in Patent Document 1 is configured by alternately stacking a plurality of piezoelectric layers and a plurality of electrode layers, and the plurality of electrode layers includes four types of electrode layers: a positive type of electrode layers in which a pair of split electrodes disposed along one diagonal direction are connected together, a positive type of electrode layers in which a pair of split electrodes disposed along the other diagonal direction are connected together, a negative type of electrode layers in which a pair of split electrodes disposed along one diagonal direction are connected together, and a negative type of electrode layers in which a pair of split electrodes disposed along the other diagonal direction are connected together.
In this way, by connecting split electrodes having a same potential together in a same electrode layer, the number of connection lines to the piezoelectric element is reduced.